1. Field of the Invention
The present invention relates to a MOS-type FET amplifier, and more particularly relates to a MOS-type FET amplifier which has an excellent switching speed.
2. Description of the Prior Art
In the art, a class-D amplifier using a field effect transistor has been proposed by the same assignee of the instant application.
For example, the U.S. Pat. No. 4,021,748 entitled in "Amplifier with Field Effect Transistors having Triode type dynamic characteristics" shows such a class-D power amplifier.
However, as such a triode type field effect transistor is normally a depletion type transistor, it would have a rather complicated drive stage. On the other hand, a MOS-type field effect transistor has recently developed for a power amplifier use which has large drain current capability and higher drain breakdown voltage. Such a MOS-type FET is known as an enhancement type transistor, in which it would be possible to simplify a drive circuit as compared to that of the depletion type FET. In general, a MOS-type FET is also required to electrically connect its substrate to the source electrode in order to stabilize the potential thereof. Such a connection would provide a PN junction between drain and source electrodes through a substrate so as to deteriorate the switching speed thereof in the case of class-D amplifying mode.